1. Field of the Invention
This invention relates to an apparatus for floating and sinking fish breeding netted tanks.
2. Description of the Prior Art
In the sea age of 200 sea miles, breeding industry for fishes and shellfishes is becoming ever developing. The conventional fish breeding netted tank is composed of a raft framework adapted to be floated on the sea and surrounded by a netted body. Such conventional fish breeding netted tank is very simple in construction. As a result, if it is used in the ocean in which the waves are high, the raft framework tends to be easily broken. In addition, it is impossible to sink the fish breeding netted tank deep under water, thereby weakening the fishes in the fish breeding netted tank. Thus, such conventional fish breeding netted tank could not be used in the ocean and the use thereof is limited to that sea region which is inside a bay or along the shore, and as a result, there is a risk of oxygen being decreased or the sea long the shore being polluted by decaying ground-bait.
In order to render it possible to use the fish breeding netted tank in the ocean, it has been required to avoid the damage subjected to it when it is used when the weather is rough. For this purpose, various kinds of apparatus for floating and sinking the fish breeding netted tanks have been developed.
In one of such conventional apparatus, the fish breeding netted tank is suspended from a supporting frame composed of adjustable float chambers adapted to be alternately filled with air and sea water for the purpose of floating the supporting frame on the sea surface and of sinking it deep under water. Such frame-shaped float chambers are small in height, so that in the case of replacing the air by the sea water or the vice versa, the left and right float chambers become easily unbalanced. As a result, when the float chambers are operated to be floated and sunk, the fish breeding netted tank becomes unstable and swings. In addition, there is a risk of a fitting portion of an air inlet and outlet pipe being removed from the float chamber.
In addition, a fish breeding technique which is high in yield has recently been required to be developed. For this purpose, the fish breeding netted tank must be large in size. In the conventional fish breeding netted tank in which the strength against the waves or the like is dependent on the rigidity of the supporting frame, if the fish breeding netted tank is made large in size, the strength of the supporting frame must also be made excessively large and hence the supporting frame becomes expensive. Thus, the practical use of such large type conventional fish breeding netted tank has been limited.
In addition, if the fish breeding netted tank is totally covered with a netted body and that portion of the netted body which constitutes a ceiling is located on the water surface, such netted portion not only prevents ground-bait from scattering for the fishes but also becomes easily broken.
In another conventional apparatus for floating and sinking fish breeding netted tanks, a float chamber composed of an elongate flexible bag is suspended from a supporting frame with the lengthwise direction of the flexible bag made vertical. In such conventional apparatus, if the fish breeding netted tank is refloated from its sunken state and the water pressure difference between the upper and lower portions of the flexible bag causes the lower portion to expand under a pressure which is higher than a required pressure, the upper portion becomes excessively expanded. In addition, if the fish breeding netted tank is caught in obstacles in the sea and could not be refloated from its sunken state, there is a risk of the flexible bag being broken by excessive air supplied thereinto for the purpose of refloating it by mistake that the flexible bag is in need of added buoyancy.